The present invention relates to polymer embedment of rails for railway lines.
With the reintroduction of street tramways (light railways) in the UK and the upgrading and extension of existing tram networks world wide, there is a continual need to improve products and methods of installation to keep in line with various installation requirements and to be able to compete within the market place.
It is no longer acceptable for tramlines to be noisy, cause vibration in surrounding structures or to damage the statutory undertaker pipes, cables or ducts due to corrosion from stray electrical currents running through the rails.
At present the method of fixing a rail into the street requires the following to be taken into account. Firstly, the rail must be held extremely securely in its correct position. Standardly, this is done by providing a track bed into which the rail line is positioned for fixing. This may cause difficulties in positioning the rail and maintaining that position while the rail is fixed into the street. Secondly, the method of fixing the rail must provide for reduction in both noise and vibration caused by the trams along the lines and also prevent any stray electrical current passing from the rail in to the neighbouring surroundings. Thirdly, because the rail lines are fixed into the street it is important that the method of fixing and the form of fixant used does not cause a hazard to other street users.
Many track bed construction methods are available to fix the rail into the correct position in the street but, many of these systems fail to fulfill the above mentioned requirements.
There are, however, two distinct methods which go part way to satisfying the requirements, namely a) provision of pre-vulcanised rubber sections that are fitted around the rail; and b) the use of liquid polyurethane rubber which is poured around a preinstalled rail to fully encapsulate the rail.
Although the pre-vulcanised rubber section method provides a lower installation cost the poured polymer method comes closer to fulfilling the requirements of rail line fixing.
The poured polymer system requires a concrete track slab to be formed into which two slots that hold the rails have been preformed. The track slab has to be formed very accurately as the position of the slots determines both the final vertical and horizontal alignment of the top of the rail. That alignment is also dependent on the roadways and streets surrounding the track slab, and this means that the positioning is an extremely difficult task. Variations in the slot width or depth results in the increase in the amount of polymer being used, hence cost.
For the system to work effectively the poured polymer must bond to the rail and the concrete slot. Before the polymer is applied, both substrates must be dry and therefore the entire working area must be protected from the wet weather.
It is possible with poured systems to add to the top layer of the polymer, i.e at the road surface, a variety of anti-skid materials e.g. bauxite or granite chippings. However, in order to prevent the heavier anti-skid materials from sinking into the polymer away from the surface, they have to be added in a separate top layer of polymer once the rest of the polymer has started to solidify.
In order to address these problems, the applicants have decided to depart from the existing poured polymer systems, by coating the rail with a poured polymer with the rail in a mould, and then curing the polymer in the mould, enabling the rail to be coated off-site. Furthermore, the rail is coated in the mould when the rail is inverted, ie. the head of the rail is at the bottom of the mould.
This method has several advantages. Firstly, because the rail is inverted, the mouth of the mould corresponds to the foot of the rail, which in general is wider than the head of the rail. Thus, the mould can be shaped to minimise the amount of polymer needed, and yet have a wide mouth to permit the polymer to be poured in easily.
Secondly, the fact that the rail is coated in the polymer off-site by a poured polymer arrangement means that there is chemical bonding of the polymer to the rail, as in the existing on-site arrangements, but the coating of the rail may be carried out in factory-controlled conditions.
It may be possible for the concrete slot known in prior art methods to be considered the xe2x80x9cmouldxe2x80x9d described is the method which in the first aspect of the invention. If this is so, the coated rail is never removed from the xe2x80x9cmouldxe2x80x9d in these prior art methods.
If anti-skid materials are to be added into the mould, they can be added before the polymer is poured in and they will rest naturally by gravity at the bottom of the mould, and thus be in the polymer adjacent the head of the rail without requiring successive layers of polymer.
It should be noted that, since the polymer is an expensive component in the present invention, it is preferable that the mould is shaped similar to keep small the amount polymer needed. Many different mould shapes are possible, including those which conform generally to the profile of the rail, and also including arrangements in which the mould tapers towards the head of the rail.
Also, it is possible to make use of ballast blocks attached to the rail using eg. an epoxy resin. Such ballast blocks are known in the art, and assist in the attenuation of noise and vibration. In the present invention, they also have the added advantages of filling part of the hollow interim of the mould, so reducing the amount of polymer needed. For the sake of convenience in this specification, such ballast blocks are considered optional parts of the xe2x80x9crailxe2x80x9d, so that the xe2x80x9crailxe2x80x9d includes structures where such ballast blocks are present, as well as those where they are not.
First, in order to install a rail line in a track bed, the rail will be coated with a poured polymer in a mould, with the rail head-down in the mould, the coated rail is transported to the site in which it is to be positioned with or without the mould in place, the mould is removed, and the rail and coating (which is now solid) is mounted on a track bed and fixed thereto for subsequent use.
The track bed may have two parallel slots therein, to receive two coated rails, but it is preferable to use a flat track bed, of eg. concrete with the coated rails being held apart by tie-rods whilst they are secured to the track bed. A further layer of eg. concrete may then be formed on the track bed, to embed the coated-rail. In a development of this, that additional layer of concrete does not extend to the top of the head of the rail; instead it extends parts of the way up the rail and a layer of eg. asphalt is then placed on top of the concrete. In such an arrangement the head of the rail is at the ground surface when in place. This is particularly useful in a light railway where the tracks run in a road to be used by other vehicles.
Thus, in order to coat the rail blocks, they may be held within a mould generally complementary to the perimeter of the rail block so as to minimise the amount of polymer required within the mould to coat the rail block. Once positioned within the mould the polymer is poured in so as to cover the rail and allowed to set into a solid. The mould is then removed and the rail block is ready for installation.
By inverting the rail block within the mould, in other words placing the head of the rail upon which the tram will run at the base of the mould, anti-skid material may be poured into the mould before the polymer is poured in. In this way there is no need for a separate process step and the risk of the layer containing the anti-skid material separating from the remaining polymer coating is dramatically reduced.
The present invention relates to a method of coating a rail as discussed above, and also to a coated rail thus formed. Although the present invention has been developed for rails to be used in light railways, or tram systems, where the rails are mounted in a road to be used by other vehicles, the present invention is not limited to this and may be used for any rail system. The invention may also be applied to curved rails, such as transition rails.